Dumortier's superb form earns him first France cap for Six Nations opener
The 22-year-old Lyon wing has scored 11 tries this season - eight in the Top 14 and three in the Champions Cup - and the sevens specialist gets his chance due to the injury to Gabin Villiere.
"He made a strong impression when he came to work with us," said head coach Fabien Galthie.
"We wanted him to evolve like this, as is the case with his club Lyon and now with us."
Dumortier's debut aside the rest of the starting XV features many of the key players in France's Grand Slam success last year with the 2023 Rugby World Cup hosts on a 13 match winning streak.
Scrum-half Antoine Dupont, the 2021 World Player of the Year who captains the team, forms a formidable half-back partnership with fly-half Romain Ntamack.
Galthie said despite the title last year and the many compliments about their playing style he and the players were not going to rest on their laurels after three years of hard work.
They have their crown to defend but that is the first course before the main one later in the year trying on home soil to become the first France side to lift the World Cup trophy - they have lost three times in the final.
"We were second in the preceding two Six Nations tournaments before we won," he said.
"We believe that the journey is far from over. We will only get better, we will continue to make progress.
"Our team is still not fully mature in terms of test rugby, agewise, caps or experience.
"Whatever happens in the tournament results wise we will make progress."
Galthie, 53, said he expected no presents from Italy who have shown a marked improvement since Kieran Crowley took over as head coach - beating Wales and Australia last year.
"We have left little to chance, preparing for chaos and all the possible scenarios," said the former France scrum-half and captain.
"A magnificent Italian side, who are reaping the rewards.
"They are a sublime opponent, it is an extraordinary challenge."
Galthie and his coaching staff also displayed their gratitude to former French Rugby Federation (FFR) president Bernard Laporte.
The 58-year-old resigned last week after being convicted of corruption in December.
However, France's rugby manager Raphael Ibanez said they had invited him to a gathering on Thursday evening.
"Our ambitions are purely sporting ones and nothing to do with the political machinations," he said.
"Yesterday evening we invited Bernard Laporte to join us: the World Cup is being organised in France, that is down to him.
"The current set up, the training conditions and the staff is also down to him."
Laporte has been replaced it was revealed on Friday by the FFR treasurer Alexandre Martinez, who will be acting president until the federation's general assembly in Lille in June.
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Team (15-1)
Thomas Ramos; Damian Penaud, Yoram Moefana, Gael Fickou, Ethan Dumortier; Romain Ntamack, Antoine Dupont (capt); Gregory Alldritt, Charles Ollivon, Anthony Jelonch; Paul Willemse, Thibaud Flament; Uini Atonio, Julien Marchand, Cyril Baille
Replacements: Gaetan Barlot, Reda Wardi, Sipili Falatea, Romain Taofifenua, Thomas Lavault, Sekou Macalou, Nolann Le Garrec, Matthieu Jalibert
Coach: Fabien Galthie (FRA)
